I have seen several airports (YVR and SLC come to mind) where your BP is scanned at the podium, and as you proceed down the jetway there are several sub-gates leading to different aircraft. These are designated e.g. 28A, 28B, 28C, etc. It is a fairly easy thing to enter the wrong gate and wrong aircraft if no one is paying attention.

Once, ~10 years ago in SLC pax were scanned and directed to a certain gate, only to find the aircraft hadn't arrived yet .